The Influence of Ridge Subduction on the Geochemistry of Vanuatu Arc Magmas

Deng, Chen; Jenner, Frances E.; Wan, Bo and Li, Ji‐Lei (2022). The Influence of Ridge Subduction on the Geochemistry of Vanuatu Arc Magmas. Journal of Geophysical Research: Solid Earth, 127(1), article no. e2021JB022833.



The effects of buoyant ridge subduction have been researched for decades. However, it remains unclear how this process influences magma chemistry. Here we use a compilation of geochemical data, well-established geochemical proxies (i.e., Ba/Nb, Th/Nb) and mantle redox modeling (i.e., V/Sc, Cu) to propose that the subduction of a ridge underneath the central portion of the Vanuatu arc causes shallow-angle subduction and the development of a slab tear. We suggest that the shallow slab pinches out the asthenospheric mantle and bulldozes ancient metasomatized lithospheric mantle from the forearc toward the main-arc. Slab-fluxed melting of this bulldozed material could account for the along-arc 87Sr/86Sr-143Nd/144Nd variations of the Vanuatu magmas. The influx of hot sub-slab material into the Vanuatu arc mantle wedge through a slab tear produces magmatism within the forearc. Modeling of V/Sc and Cu systematics suggest that the mantle source of the forearc magmas has a higher fO2 and Cu content than the source of the main-arc and rear-arc samples. The main-arc and rear-arc mantles were metasomatized by both slab-derived fluids and melts. Whereas release of high Cu-SO2 slab-derived fluids caused oxidation and Cu enrichment of the forearc mantle. These systematics indicate a decrease in the fO2 of slab fluxes with increasing depth-to-slab and distance-from-trench. Our findings highlight the role of ridge subduction in controlling the along-arc and across-arc variations in the chemistry of Vanuatu arc magmas. This updated geodynamic model, based on geochemistry, is consistent with recent geophysical constraints and 3D numerical modeling.

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